Flame-retardant particle-board and process for making same

ABSTRACT

High flame retardancy is imparted to particleboard by treating it in the course of fabrication with a combination of alkaline borate chemicals and flame-retardant phosphoric aciddicyandiamide-formaldehyde resin. The alkaline borate chemicals, e.g., borax and boric acid, are dissolved and added to the wood chips prior to their conversion into flake form. Next the flameretardant resin, comprised of phosphoric acid, melamine or urea, dicyandiamide and formaldehyde, is added to the comminuted wood flakes, either before they are dried or, following drying, at the blender at which a bonding resin such as urea resin is mixed preparatory to the forming of the mixture into mats and its pressing into panels.

111 1 fleet 119 312 United States Patent 1191 1111 3,874,990 Surdyk 1 Apr. 1, 1975 1 FLAME-RETARDANT PARTICLE-BOARD 3.321.421 5/1967 Pataki 161/403 AND PROCESS FOR MAKING SAME 3,383,274 5/1968 Galg 3,438,847 4/1969 Chase Inventor: y y ster, Callf- 3,649,397 3/1972 Peters [73] Assigneez Collins Pine p y Portland, 3,832,316 8/1974 June a 117/148 Ore g Primary Examiner-George F. Lesmes 1 1 Flledi J 1973 Assistant E.\'aminerE. P. Robinson 211 App]. N 3 9 770 Attorney, Agent, 0/ Firm-Chernoff & Vilhauer 52 US. Cl. 161/261, 106/15 FP, 117/137, [57] ABSTRACT 161/168, 161/403, 161/270, 260/15, High flame retardancy is imparted to particleboard by 260/17.3, 264/122, 264/128 treating it in the course of fabrication with a combina- [51] Int. Cl. B32b 5/16, B32b 21/02 tion of alkaline borate chemicals and flame-retardant [58] Field of Search 161/403, 162, 168, 261; phosphoric acid-dicyandiamide-formaldehyde resin. 117/137; 264/115, 128, 122; 260/15, 17.3, The alkaline borate chemicals, e.g., borax and boric 260/DIG. 24; 106/15 FP; 252/8.1 acid, are dissolved and added to the wood chips prior to their conversion into flake form. Next the flame- [56] References Cited retardant resin, comprised of phosphoric acid, mela- UNITED STATES PATENTS mine or urea, dicyandiamide and formaldehyde, is 7 added to the comminuted wood flakes, either before 52331223 11132? 31112121111:1:31:13311111131313?22111 793 they e fellewldg deyldg, el the blender ed 21628,)46 2 1953 .luda 161/261 which a bonding resin Such as urea resin is mixed P 2,917,408 12/1959 Goldsr i 117/137 paratory to the forming of the mixture into mats and 3,137,607 6/1964 Goldstein... 161/403 its pressing into panels. 3,159,503 12/1964 GOldStCln 1. 117 137 3,213,045 10/1965 Klein 161/262 4 Clams, 1 Drawmg Flgure' 2nd Fire-Retardant Additive (Phosphoric acid-formaldehydedicyandiamide resin) lst Fire-Retardant Additive (Alkaline Borate Chemicals) W11 (chips or pagticles) L 4 B 7 6 9 2 water spray I Bonding llW-ml resin I Wax Stabilize: (optional) FLAME-RETARDANT PARTICLE-BOARD AND PROCESS FOR MAKING SAME BACKGROUND OF THE INVENTION The present invention is directed to flame-retardant particleboard and, more particularly, to a particleboard product having satisfactory Structural integrity and strength for widespread application yet possession sufficient flame-retardant characteristics to meet Underwriters Laboratories test standard 723 for Class I building materials.

Formulations for imparting flame-retardant characteristics to particleboard utilizing either alkaline borate chemicals or phosphoric acid-dicyandiamideformaldehyde impregnating solutions are known to the prior art. For example Chase US. Pat. No. 3,438,847 and Pataki et al. US. Pat. No. 3,321,421 each disclose the use of borate chemicals, such as sodium borate, sodium tetraboratc or the like, for mixing with a urea formaldehyde or melamine formaldehyde bonding resin to impart flame-retardant characteristics to the comminuted wood flakes as they are fabricated into particlcboard panels. Similarly, Goldstein et al. US. Pat. No. 3,159,503 discloses a formulation for imparting fireretardancy to particleboard utilizing an impregnating solution comprised of phosphoric acid, dicyandiamide and formaldehyde. Finally, an article by S. C. .luneja entitled Stable and Leach-Resistant Fire Retardants for Wood published in the June 1972 issue of Forest Products Journal, Vol. 22, No. 6, pp. 17-23, describes a fire-retardant resin formulation for particleboard comprised of melamine, dicyandiamide, phosphoric acid and formaldehyde.

While the aforedescribed prior art borate chemical and phosphoric acid-dicyandiamide-formaldehyde formulations are effective for the purpose of imparting good flame retardancy characteristics to comminuted wood flakes or chips, it has been found that, when such formulations are applied in effective amounts so that the resulting board product cansuccessfully pass the Underwriters- Laboratories standards for Class I buliding materials, the press time for fabrication of the board is unduly lengthened and/or the strength, stability and other desirable physical characteristics of the board are deteriorated by the fire-retardant additives to the point that the board product is no longer suitable for many commercial applications. Furthermore, phosphoric acid-dicyandiamide-formaldehyde resin, while superior in certain respects to the borate chemical formulation, is corrosive and considerably more expensive when used in amounts sufficient to impart an equivalent degree of fire retardancy to the final board product. For these reasons the particleboard industry has been endeavoring for a number of years to develop an economical fire-retardant formulation, with which the comminuted wood particles can be impregnated in the course of their fabrication into particleboard, which would not materially lengthen the press cycle nor substantially weaken the board's desirable physical characteristics and yet would satisfy Class 1 fire retardancy standards and be widely usable for commercial applications interchangeably with untreated particleboard.

SUMMARY OF THE INVENTION The present invention provides a process and formulation for treating particleboard to impart high flameretardant characteristics (sufficient to comply with UL 723 test standards) and overcomes the aforementioned disadvantages of the prior art formulations by utilizing a combination of alkaline borate chemicals and phosphoric acid-dicyandiamide-formaldehydc resin, the proportion of each additive being maintained within predetermined ranges so that the fabrication time of the particleboard is not significantly prolonged and the resulting board product possesses satisfactory physical characteristics. The fire-retardant additives can be incorporated into a conventional particleboard fabrication process by the introduction of the constituent chemicals at appropriate stages in the process cycle as will hereinafter be more fully described.

In the preferred formulation, the comminuted wood is impregnated with the fire-retardant additives in an amount of 10 to 1671 calculated solids based on the oven dry weight (BDW) of the wood, the additives preferably being 3% by weight of a fire-retardant resin comprised of phosphoric acid, dicyandiamide, formaldehyde andmelamine (or urea) and the balance of from 7 to 13% by weight being alkaline borate chemicals, exemplarily a mixture of borax and boric acid.

DESCRIPTION OF THE DRAWING The single FIGURE is a flow diagram illustrating the process for fabricating fire-retardant particleboard in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the flow diagram which illustrates the manufacture of fire-retardant particleboard panels in accordance with the present invention, comminuted wood particles 2, either in the form of dry or green wood chips, flakes or planer shavings, or combinations thereof, and comprised of sugar pine, ponderosa pine, white fir or other wood species having a moisture content ranging from about 8% to 250%, are conveyed in metered amounts from a surge bin or storage silo on a conveyor 4 to a flaker 6 which comminutes the wood into flake form, Prior to the rendering into flakes and while the wood is carried on the conveyor 4, alkaline borate chemicals 5 are added to the wood material. In the preferred embodiment the borate chemicals are in the form of Polybor which is a proprietary borax-boric acid mixture in the ratio of 5 to 3 manufactured by US. Borax Company. Alternatively, sodium tetraborate, sodium octoborate or other borate chemicals in combination with an inorganic acid such as boric acid or hydrochloric acid could be used at this first additive station 5. The alkaline borate chemieals are discharged in dry form onto the top of the wood material as it is conveyed on the conveyor 4 and, to insure their subsequent infusion and impregnation of the wood particles, it is desirable that an aqueous environment be provided in the form of a fine water spray 7 for wetting the wood material and the deposited borate chemicals.

The wetted-down borate chemicals 5 and comminuted wood material 2 are then conveyed to the flaker 6 where the wood particles are sliced into flakes and the natural moisture present in the wood, as well as the added water from the spray, dissolves the borate and helps it to diffuse throughout the entire mass of the wood flakes. The flakes, now thoroughly diffused with the borate, are carried on conveyor 8 to a drier 9 where the mixture is dried to a uniform moisture content between 3% and 5% BDW. The dried flakes are metered to a blender 10 where a suitable bonding resin 12, exemplarily urea or melamine formaldehyde ranging from 2 to 8% BDW of the borate-infused wood, is added. The second fire'retardant additive, in the form temperature all of the alkaline chemicals would be fully dissolved in solution, thus insuring that the solution has the necessary slight alkalinity to subsequently react satisfactorily with the melamine (or urea) and dicyandiof a phosphoric acid-formaldehyde'dicyandiamide 5 amide. Thereafter 63 grams of melamine (or urea) and resin 11, is introduced and mixed with the wood chips, 126 grams of dicyandiamide are mixed together and either at the blender where the bonding resin is inadded slowly to the alkalized formaldehyde solution troduced, or alternatively, and preferably, after the under constant stirring and with the 176 F. temperaflaker 6 but prior to drying. One suitable method of inture maintained. After all the melamine-dicyandiamide troduction would be to spray the dicyandiamide- 1() has been added, the solution is cooled to 70 F. and formaldehyde resin and phosphoric acid onto the wood then 465 grams of 7571 phosphoric acid is added to the particles utilizing a two-component atomizing nozzle. resin so formed. The resin produced has approximately After the blending station 10 the flakes containing the following ratio of molecular weights: 0.5 moles of the two fire-retardant additives 5 and 11, as well as the melamine, 1.50 moles of dicyandiamide, 4.00 moles of bonding resin 12, are then conveyed to the forming formaldehyde and 3.56 moles of phosphoric acid, with equipment l3l5 where the material is formed into sufficient borate or other base material to adjust the pH mats and pressed under heat and pressure into panels. of the resin to approximately 8 (slightly alkaline). Thereu on the boards IIC cool d, stacked for ip Add Based upon the bone dry weight of the wood, the tional cooling and sanded to uniform smoothness and total calculated solids content of the two fire-retardant thickness, as is conventional. To improve the dimeni additives he within the range of 10-16%, with the bosional moisture stability of the resulting board product,

. rate chemical additive constituting no less than about a suitable wax 17 in emulsion or molten form can be 0 8 /Z- and the resin additive being in the range of 1% to added if desired to the wood particle mix at the blender 8%. The preferred proportions for producing Class 1 station 10 or elsewhere in the fabrication process. i

. flame-retardant particleboard with the most desirable While the aforedescribed process has been directed properties are 3% phosphoric 21C1dd1Cy2lnd1Zlm1Cl6 to the fabrication of a homogeneous, single-layer partiformaldehyde resin and 13% borate chemicals, e.g., cleboard panel, it will be understood that, if dCSlI'Cd, I three-la er fire-retardant bo'ird com rised of '1 core Polybor bordx b0nc dud mlxture' wlth hlgher percent h r f l t ages of borate to phosphoric aeid-dicyandiamidefi f 2: 9 S ch 3 g w formaldehyde resin than the preferred relationship set Si 7 g z z f g f c forth above, longer press times are required and the mm c y 1 0 I O strength and stability of the resulting board product are elude an extra mat forming heads so that both face and d eleteriously affected. Conversely, with higher percore material mats, treated with the tire-retardant for- I f h h I t mulation of the resent invention are roduced ind cemdges O p 05p one Cyan p p 3g formaldehyde resin, while the press cycle for forming then assembled for pressing into panels.

A f I f t Y b t h the board is reduced because the bonding resin cures n cxl'mp My (.mnu or .urm K more rapidly due to the higher acid content of the mixot the phosphoric acidformaldchyde-dicyandiamide ture, the strength of the resultant board product is maresin which is provided at the second fire-retardant adterially reduced and the surface appearance of the ditivc station in the atorcdescribed process would be as board is less satisfactory follows: 324 grams of 37% formaldehyde solution are 40 mixed with approximately 40 grams of Polybor borate In a laboratory test run, samples of homogeneous, chemicals to adjust the solution to be slightly alkaline, single-layer particleboard panels of 15 inches X 17 about pH 8. (As an alternative to the Polybor borate, inches X /2 inches dimensions were made "containing sodium hydroxide, sodium carbonate, ammonium hy- 5 various amounts of the two fire-retardant additives redroxide or other suitable alkaline material could be ferred to above and were found to have the flameused to alkalyze the formaldehyde solution.) The soluretardant, strength and other physcial characteristics as tion is then heated to approximately 176 F. at which set forth in the following table.

. Minimum Flame Modulus Modulus Internal Water Thickness Sample Press Time Spread of Rupture Elasticity Bond Strength Absorption Swell (:roup (minutes) (inches) (PS1) (PSIXHF') (PS1) Moisture) A. 16'?! Polybor PDF resin 7 9 1750 511 107 1 B. 13% Polybor I6 79 071 PDF resin 6% 11 1753 381 110 114 58 C. 10% Polybor 0'71 PDF resin 6 13 1751 392 114 111 60 D. 1571 Polybor 1'7: PDF resin 4 9 1905 490 124 109 61 E. 14% Polybor 27: PDF resin 3V2 9 2195 557 133 91 42 F. 13% Polybor 3% PDF resin 2% 9 2462 516 113 87 30 G. 127: Polybor 4'7? PDF resin 3 9 2240 571 138 84 33 H. 117: Polybor 591 PDF resin 3 10 2245 529 123 86 37 1. 107: Polybor 671 PDF resin 2% 10 1970 457 131 86 37 PDF" Phosphoric aciddieyandiamide-formaldehyde-melamine A urea resin was used as the bonding agent for all board samples. Minimum press time was defined for purposes of the test run as that minimum time (including closing time of the press) at which the springback of the nominal /2 inch board thickness, immediately upon release from the press (press temperature 320 F. was less than 0.010 inch. For testing flame spread, strength and other properties of the board material, all samples were pressed for 5 minutes except for specimens in groups A. B and C (borate chemicals alone) which required ten minutes press time in order for the bonding agent to cure sufficiently to hold the board together.

The terms and expressions which have been employed in the foregoing abstract and specification are used therein as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding equivalents of the features shown and described or portions thereof. it being recognized that the scope of the invention is defined and limited only by the claims which follow.

I claim:

I. A process for manufacturing fire-retardant composite wood products comprising: forming comminuted wood particles; diffusing into said wood particles a fireretardant alkaline b9 rte chemical; adding to said wood particles a formaldehyde resin formed from formaldehyde, dicyandiamide, phosphoric acid and a reactant selected from the group consisting of urea and melamine; blending a curable bonding resin with said wood particles; and compressing said wood particles with sufficient pressure and temperature to cure the bonding resin to form a composite wood product.

2. The process according to claim 1 further including the step of drying the wood particles before the bonding resin is blended therewith.

3. The process according to claim 1 wherein said curable bonding resin is selected from the group consisting of urea-formaldehyde and melamine-formaldehyde.

4. A fire-retardant composite wood product formed by the process in claim 1.

UNIFIED STATES PATENT AND TRADEMARK OFFICE QERHFTCATE OF CORRECTION PATENT NO.

DATED rNveNrorzrs) 3,874,990 April 1, 1975 Lyle V. Surdyk it is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

C01. 1 Line 41 C01. 2, Line 50 In the Table at the bottom of Columns 3 and 4 [SEAL] In the row listing Sample Group A, before "PDF resin" insert O%-.

Signed and Scaled this sixth Day of Aprill976 A ltest:

RUTH C. MASON Arresting Officer C. MARSHALL DANN C nmmissinner oflatents and Trademarks 

1. A PROCESS FOR MANUFACTUREING FIRE-RETARDANT COMPOSITE WOOD PRODUCT COMPRISING: FORMING COMMINUTED WOOD PARTICLES, DIFFUSING INTO SAID WOOD PARTICLES A FIRE-RETARDANT ALKALINE BORATE CHEMICAL, ADDING TO SAID WOOD PARTICLES A FORMALDEHYDE RESIN FORMED FROM FORMALDEHYDE, DICYANDIAMIDE, PHOSPHORIC ACID AND A REACTANT SELECTED FROM THE GROUP CONSISTING OF UREA AND MELAMINE, BLENDING A CURABLE BONDING RESIN WITH SAID WOOD PARTICLES, AND COMPRESSING SAID WOOD PARTICLES WITH SUFFICIENT PRESSURE AND TEMPERATURE TO CURE THE BONDING RESIN TO FORM A COMPOSITE WOOD PRODUCT.
 2. The process according to claim 1 further including the step of drying the wood particles before the bonding resin is blended therewith.
 3. The process according to claim 1 wherein said curable bonding resin is selected from the group consisting of urea-formaldehyde and melamine-formaldehyde.
 4. A fire-retardant composite wood product formed by the process in claim
 1. 